The illumination of a large area by a central lighting system has long been desired because of its many advantages. For example, a centralized light source is easier to maintain than many separate light sources, heat generated by a centralized light source can be easily vented from the lighted areas, whereas heat from distributed light sources is not easily vented, and a light distribution system connected to a centralized light source radiates minimal or no heat. One such system utilizes a light guide luminaire to transmit and distribute the light.
Prism light guides and light guide luminaires are known in the patented prior art. The Whitehead U.S. Pat. No. 4,260,220, for example, discloses a hollow longitudinal light guide structure made of transparent dielectric material, such as acrylic plastic or optically clear glass, for transmitting or "piping" light from a central source to a remote location. The light guide includes substantially planar inner and outer surfaces which are in "octature." The light guide is formed of one or more longitudinal sections, each preferably having a constant cross-section along its length. The light guide can have a hollow rectangular or square cross-sectional structure made of four longitudinal wall sections bonded to form corners. The light guide can include an outer jacket or cover to protect the outer surface of the dielectric material from damage. The corners of the light guide are held in the protective jacket by corner strips and strip springs.
The Whitehead U.S. Pat. No. 4,615,579 discloses a luminaire for a prism light guide system including a light release mechanism for releasing light along the length of the light guide. The light release mechanism can be a non-planar surface, a rough outer surface, or round corners in an outer corrugated surface. The Whitehead U.S. Pat. No. 4,787,708 discloses a variety of additional techniques for continuously controlling the emission of light from a light guide such that, for example, the amount of light escaping per unit length along the light guide can be made constant to provide uniform illumination. To reflect any escaping light back into the luminaire so that it can be released through the desired surface, all of the outer surfaces through which it is not desired to have light escape can be covered by a highly reflective diffuse material such as a mirror, white paint, white plastic, white paper, or white fabric.
Light guides and light guide luminaires may be constructed with a variety of cross-sectional shapes as disclosed in U.S. Pat. No. 4,260,220 (Whitehead), U.S. Pat. No. 5,661,839 (Whitehead), U.S. Pat. No. 5,715,347 (Whitehead), and U.S. Pat. No. 4,805,984 (Cobb, Jr.). In addition, light guides can be constructed using a variety of materials such as transparent dielectric materials including acrylic plastic or optically clear glass as disclosed in U.S. Pat. No. 4,260,220 (Whitehead), or multilayer optical films as disclosed in U.S. Pat. No. 5,661,839 (Whitehead).
A typical light guide luminaire according to the prior art is depicted in FIG. 1. The luminaire 2 has a circular cross-section and includes an outer shell 4, a back reflector 6 fitted tightly against a portion of the inner surface of the shell 4, and optical lighting film 8 arranged adjacent the back reflector 6. The optical lighting film 8 is a continuous sheet of film and includes an extractor material 10 applied directly to the inner surface of the film 8 prior to assembly. Thus, the luminaire 2 includes a back reflector 6 which is tightly sandwiched between the outer shell 4 and the optical lighting film 8 with its entire inner and outer surfaces in contact therewith. The optical lighting film 8 is frictionally held in place due to the force created by bending the film and inserting it into the outer shell 4.
Conventional light guide luminaires, however, have a number of limitations and drawbacks. For example, by having the optical lighting film, back reflector, and outer shell in close contact, conventional light guide luminaires are prone to having condensation collect on the inner surface of the optical lighting film, thereby causing disruption in the light path which results in the unwanted extraction of light. In addition, having the optical lighting film, back reflector, and outer shell in close contact prevents these components from being individually slid into and/or out of the light guide luminaire without being damaged. That is, when the luminaire is constructed such that the optical lighting film, back reflector, and outer shell are in contact with one another, sliding movement among these components can cause the optical lighting film and back reflector to be scratched, thereby significantly impairing the performance of the luminaire. Accordingly, with conventional light guide luminaires, removal, replacement, or modification of the optical lighting film, back reflector, or outer shell requires complete disassembly of the luminaire.
In addition, the diameter of conventional light guide luminaires is limited depending on the flexibility of the optical lighting film used to construct the light guide. That is, certain commercially available materials with desirable optical properties presently cannot be used to construct small diameter light guide luminaires because the material is rigid and tends to crack when rolled into a cross-section having a small radius of curvature. A light guide luminaire constructed of a commercially available polycarbonate optical lighting film, for example, will begin to crack when formed into a light guide having a diameter of less than approximately four inches. As explained in U.S. Pat. No. 5,745,632 (Dreyer), an approximation for the minimum cylindrical diameter to which a particular film may be curled is determined by the equation: D=T.times.C, where D is the diameter of the film, T is the thickness T of the film as measured from the smooth surface to the valley of the grooves, and C is a constant associated with the modulus of elasticity of the particular material.
Conventional light guide luminaire systems are typically constructed to a desired length and may be made in separate sections for handling and shipping ease. More recently, modular light guide luminaire systems have been developed utilizing a number of separate modules which are joined to form a chain as described in U.S. Pat. No. 5,901,266 (Whitehead). Each module is the same except for the extractor which must be sized to ensure the proper amount of light is emitted from each module depending on the location of the module within the chain. Since each module is constructed before it is assembled into a light distribution chain, a large inventory of modules, each having a specifically sized extractor, must be maintained to construct a light distribution system. Thus, current light guide luminaire systems must be designed for their intended end use application and once assembled, cannot be easily modified.
It would therefore be desirable to provide a light guide luminaire capable of being formed into relatively small cross-sectional configurations regardless of the material used to form the light guide. It would also be desirable to provide a light guide luminaire having air gaps between the optical lighting film guide, back reflector, and protective outer housing to prevent moisture from condensing on the optical lighting film and allow the optical lighting film, back reflector, and extractor elements to be easily slid into or out of the protective housing without damaging the components. In addition, it would be desirable to provide a light guide luminaire which can be easily modified or customized to meet particular end use applications, thereby reducing the inventory of modules needed to construct different light guide luminaire systems, and eliminating the need to separately design each light guide luminaire system based on the end use application. It would also be desirable to provide a light guide luminaire which is easy to assemble and repair, and allows each component of the luminaire to be easily replaced without damaging the optical lighting film.